1. Field of the Invention
The present invention relates to a scanning device for use in reading and recording an image, and a composite light source unit comprising a number of semiconductor lasers, for use in such a scanning device.
2. Description of the Prior Art
There are known image information reading apparatus in which a sheet with image information recorded thereon is two-dimensionally scanned by a light beam, such as a laser beam, and light containing the image information (which is reflected from, transmitted through, or emitted by the sheet upon exposure to the scanning light beam) is detected by a light detector means including a multiplier phototube, or the like, so that the image information recorded on the sheet can be read out. Such image information reading apparatus have widely been employed as input devices for platemaking scanners, computers, and facsimile machines.
When a certain type of phosphor is exposed to radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays, or ultraviolet rays, for example, that phosphor stores a part of the energy of the radiation. When the phosphor exposed to the radiation is subsequently exposed to stimulating rays such as visible light, the phosphor emits light in proportion to the stored energy. Phosphor exhibiting such a property is referred to as a "stimulable phosphor". There have been proposed radiation image information recording and reproducing systems (see U.S. Pat. Nos. 4,258,264, 4,315,318, 4,387,428, 4,276,473 and Japanese Unexamined Patent Publications No. 56(1981)-11395, for example). In such a system, the radiation image information of an object such as a human body is stored on a sheet having a layer of stimulable phosphor, and then the stimulable phosphor sheet is scanned with stimulating rays such as a laser beam to cause the stimulable phosphor sheet to emit light representative of the radiation image. The emitted light is then photoelectrically detected to produce an image information signal that is electrically processed for generating image information. The generated image information is recorded as a visible image on a recording medium such as a photosensitive material or displayed as a visible image on a CRT or the like.
The radiation image information recording and reproducing system includes an image reading apparatus for reading image information from a stimulable phosphor sheet on which the image information is recorded. More specifically, the stimulable phosphor sheet is scanned by a deflected stimulating light beam in a main scanning direction, while at the same time the stimulable phosphor sheet is moved relatively to the stimulating light beam in an auxiliary scanning direction perpendicular to the main scanning direction. As a consequence, the stimulable phosphor is scanned two-dimensionally by the stimulating light beam. Light emitted from the stimulable phosphor sheet in response to the applied stimulating light beam is photoelectrically detected by a light detector, which then produces an image signal indicative of the image information.
The radiation image information recording and reproducing system also has an image recording apparatus. In the image recording apparatus, the image information thus read by the image information reading device is reproduced and recorded as a visible image on a recording sheet by scanning the recording sheet in a main scanning direction with a light beam which is modulated by the image signal. While the recording sheet is being thus scanned in the main scanning direction, it is also moved in an auxiliary scanning direction with respect to the modulated light beam.
Each of the image reading and recording apparatus includes a scanning device for deflecting the light beam in the main scanning direction. Employing a semiconductor laser as the light source for generating the scanning light beam in the light scanning device is well known. The semiconductor laser is smaller, less expensive, and has a smaller electric power requirement than gas lasers. The output laser beam of the semiconductor laser can be varied by controlling a drive current supplied to the semiconductor laser (i.e., the output laser beam can directly be modulated by an analog modulating signal). Therefore, it is not necessary to employ an optical modulator such as an acoustooptic modulator (AOM), or the like, separately from the semiconductor laser, and also to move the AOM into and out of the beam path of the semiconductor laser depending on whether the laser beam is to be modulated or not.
However, the semiconductor lasers available today have certain limitations. If a semiconductor laser is to be continuously energized, its continued output is relatively small, ranging from only 20 to 30 mW. Such a semiconductor laser cannot be used as a light source in the image reading device which requires a high-energy scanning light beam.
One solution is to combine the output laser beams emitted by a plurality of semiconductor lasers into a single laser beam with a high level of energy which can be used as a scanning laser beam. To generate such a composite laser beam, the laser beams generated by the respective semiconductor lasers are converted into parallel beams by respective collimator lenses, and then guided into close, parallel light paths along which the laser beams are applied to a light deflector.
The scanning device further includes, in addition to the light source and the optical system associated therewith, a synchronizing light source for generating a beam which synchronizes with scanning cycles over the sheet of the scanning laser beam in the main scanning direction so that the scanned spot on the sheet can be known, a synchronizing beam detector for detecting the synchronizing beam, and a synchronizing optical system for guiding the synchronizing beam from the synchronizing light source to the synchronizing beam detector. Since the synchronizing beam is used only to generate a synchronizing signal, the intensity of the synchronizing beam is low enough to be detectable by only the synchronizing beam detector. Therefore the synchronizing beam may be a laser beam generated by a single semiconductor laser, for example.
Consequently, one proposed scanning device may include a composite light source unit comprising a number of semiconductor lasers for emitting respective laser beams which are combined into a scanning beam, and a synchronizing beam light source comprising a single semiconductor laser. The scanning devices has a scanning system which includes the composite light source unit, a scanning optical system for guiding the scanning beam emitted from the composite light source unit onto the sheet, and a synchronizing system which includes the synchronizing beam light source, a synchronizing optical system, and a synchronizing beam detector. The scanning and synchronizing systems are primarily separate from each other except for a mechanical light deflector such as a rotating polygon and some optical system components which are shared by these systems.
Though the scanning and synchronizing systems share a rotating polygon and some optical system components, the entire number of parts of the scanning device is large, and the scanning device cannot be reduced in size. Various parts of the scanning device cannot be easily adjusted in order to produce a synchronizing signal which correctly monitors the scanned spot on the sheet. Even after the parts have been properly adjusted, the optical axis of the scanning device tends to become displaced.